Conservation vital to freshwater fish

Hidden below the surface of rivers and streams, freshwater fish are rarely seen and poorly understood by the average visitor to national parks. Consequently, the important role that national parks play to provide refuge to them can easily be underestimated.

Freshwater fish are the most “species poor” of the vertebrate groups in South Africa, with just over 100 occurring in our waters. Of these, a high proportion (45%) is endemic to South Africa. They have also achieved the unenviable status of having the highest percentage of threatened category red-data-listed species (25%) of all the vertebrates.

The potential importance of national parks for conserving freshwater fish is apparent if one considers that 13 of the 19 parks contain aquatic systems that collectively support 63 indigenous species, or 61% of the total found in South Africa.

Few species occur across the whole country, with most restricted to one of either the northern (Limpopo), central (Karoo) or southern (Cape) regions. Those which occur predominantly in the north are well represented in national parks (43 species), with high species diversity, particularly in the Kruger.

The number of species in parks in arid regions is far lower (eight), while only five are represented in the southern Cape.
Twenty-one of South Africa’s 48 endemic freshwater fish occur in one or more national parks. However, national parks fare rather poorly when it comes to conserving threatened species.

Only three of the 24 nationally threatened species occur within national parks, namely the Lowveld largemouth (Kruger), Berg-Breede River whitefish (Bontebok) and Eastern Cape redfin (Garden Route and Addo Elephant). They are classified as endangered by the International Union for Conservation of Nature.

Fish in general face an almost over-whelming number of threats, both to themselves and their aquatic environments. These include habitat alteration caused by practices such as dam construction; deteriorating water quality; changes in river flow caused by altered catchment run-off and increased abstraction; invasion by alien plants that can undergo explosive growth, thereby increasing water usage and, in extreme cases, smothering entire aquatic habitats; and invasion by alien fish species, which can increase predation and competition for resources.

In fact, there are only a few aquatic systems within national parks where one or more of these threats are not prominent. Yet, some relatively natural mountain streams and rivers do occur in Garden Route, Table Mountain and Golden Gate Highlands national parks.

Similarly, several seasonal rivers in Kruger and larger lake-like pans in Agulhas are relatively natural. These sites collectively support only about half of the freshwater fish species occurring in all national parks. The effective conservation of fish within national parks is fraught with problems. This is primarily because most of these rivers are only small components of much larger aquatic systems. Consequently, factors outside the boundaries of the parks, such as catchment land-use changes, wetland loss, water abstraction, pollution and alien introduction, influence river systems within parks.

Therefore conservation personnel have very little direct control over environmental changes that can detrimentally affect the fish communities under their protection.

Huge challenges remain to conserve freshwater fish effectively within rivers, and to ensure that national parks remain, or become, safe havens for this beleaguered group.

Key management actions include increased participation in decision making about land and resource use in river catchments outside parks; encouragement of minimum-flow assessments and flow management in stressed systems; water- quality management; control of existing alien fish and plant populations, and prevention of new introductions. Monitoring the efficacy of management actions is also essential.






Dr Ian Russell - SANParks scientific services

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